Five policemen were among those gunned down during the fighting Thursday in the northeastern town of Gashua, he said Friday by phone from the state capital of Damaturu. The attackers forced the bank manager to open the vault and stole 9 million naira ($56,500), he said.

The joint task force in the state Thursday said the clash killed five Boko Haram suspects and two policemen. A suspected Boko Haram ambush in neighboring Borno state, site of a weekend battle that led to as many as 185 deaths, killed two police officers, state Police Commissioner Yuguda Abdullahi said.

Authorities in Nigeria, Africa’s largest oil producer, have been battling an insurgency by Boko Haram that’s killed hundreds of people since 2009 in bomb and gun attacks in the largely Muslim north and the capital, Abuja.

The group says it wants to impose strict Islamic rule in Nigeria, Africa’s most populous nation, with more than 160 million people almost evenly split between the north and a mainly Christian south.

The United States criticized Boko Haram’s “heartless attacks” while urging Nigerian authorities to use appropriate force in the “asymmetrical battle” against “a determined foe,” Ambassador Terence McCulley said Thursday in an op-ed on the embassy’s website.

“We remain deeply concerned about reports of extra- judicial killings, illegal detention, and destruction of property by security forces,” he said. “Such acts create a deadly cycle of mistrust, harming the very citizens the security forces pledge to protect.”

Nigerian President Goodluck Jonathan’s office on April 22 said authorities will investigate whether the military complied with the rules of conduct in the Baga clash.